New energy power system operation security evaluation based on the SWOT analysis

Grid-connection of new energy is highly important in promoting the use of clean and renewable energy. However, it will bring huge risks to the power grid operation security, such as frequency stability, voltage stability, small signal stability, and transient stability, etc.,. In the study, SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis has been employed to construct 24 kinds of internal and external evaluation factors and 8 kinds of improvement strategies, for assessing operation security prospective with new energy power system of HM in China. The weights of SWOT factors are determined with the fuzzy-AHP method. Moreover, the fuzzy-MARCOS approach is used to select the most suitable strategies for power system operation security effective implementation. The reported research reveals that new energy in HM area not only has an ample potential for full development and generating electricity, but also brings operation security problems due to large-scale grid connection. Therefore, 8 kinds of improvement strategies are suggested to encourage the government to exploit and develop new resources, improve the investment pay, power generation and transmission technologies to mitigate the current energy crisis, and increase the energy security for sustainable development of the country. The methodology proposed herein is applicable with a case study concerning the operation security prospective of HM power grid, and all phases of the comparative analysis and sensitivity analysis illustrate the validity of MARCOS method. Furthermore, the ranked order of strategies is obtained as A2 > A6 > A5 > A1 > A8 > A7 > A4 > A3. The three most important strategies are A2, A6 and A5, i.e., “improving the technical establishment to encourage efficient and cheap electricity production”, “strive to build local permanent load, and reduce the risk of long-distance and high-capacity transmission”, “taking advantage of government incentives and investment to modify the irrational energy policies and energy planning”, respectively.

www.nature.com/scientificreports/ SWOT analysis. The SWOT analysis is a commonly used strategic analysis method that helps to identify the capabilities or deficiencies of an organization while considering the grid opportunities and threats for the future. However, SWOT analysis method can not quantitatively evaluate the factors, and can not objectively compare the priority between factors. Furthermore, a SWOT matrix may contain different strategies concerning its dimensions and factors, which are prepared based on strength-opportunity (SO), weakness-opportunity (WO), strength-threat (ST) and weakness-threat (WT) strategies; The strategies related to SWOT dimensions are given in Fig. 1. Some of the advantages of SWOT analysis are listed as follows: • It allows attention to the positive and negative aspects of the external and internal environment of the system; • By understanding the weaknesses, it helps to identify opportunities to take advantage of strengths and eliminate threats; • Determining the SWOT factors of the research object through group discussions provides the basis and support for the strategic decision-making; • It can be used at different levels in different industries, organizations, countries or governments, such as individual, national, organizational, and international levels.
The combination of SWOT analysis and MCDM method, such as AHP, has been used to determine the weight of each SWOT factor. Reference 40 reveals that most of the studies use the AHP method for prioritizing the SWOT factors and determining their weights, and recent studies employ the fuzzy AHP method combined with SWOT analysis and other MCDM method, such as TOPSIS, MABAC, DEMATEL, VIKOR and MARCOS. The use of AHP method for calculating the weights of SWOT factors and the need for a selection method such as MARCOS--an integrated SWOT-based fuzzy AHP-MARCOS method illustrates and their advantages are introduced next.
The integrated SWOT-fuzzy AHP-MARCOS method. Various MCDM methods developed for decision-making processes in the literature have been utilized to solve different problems concerning the decision- www.nature.com/scientificreports/ making in various areas. Moreover, MCDM methods are also widely used in the studies focusing on power system security assessment.
The AHP method. AHP is a popular MCDM technology in comprehensive evaluation research proposed by American operations research scientists in 1970s 24 . It is one of the most suitable methods for natural resource planning and environmental assessment. This method requires less quantitative data and information, and is simple and practical. The SWOT analysis method needs to be quantified by incorporating the SWOT model into a hierarchical structure through AHP method, and therefore, it is completely reasonable to use AHP method in this study. The integrated methodology. In the proposed method, AHP is deployed to obtain the criteria weights with SWOT, and MARCOS is utilized to evaluate the alternatives and select the best alternative to benefit from their strengths. The general framework and the flow of proposed integrated methodology are presented in Fig. 2.

Proposed methodology
This section elaborates the computational steps of the integrated SWOT-fuzzy AHP-MARCOS methodology 39 .
Step 1: Construct the SWOT matrix and factors determined by the experts.
Step 2: Construct a hierarchical structure concerning the goal and SWOT factors.
Step 3: Obtain the judgments of the experts: determine the priorities of the criteria using the linguistic terms given in Table 1. A Fuzzy comparison matrix Ã is constructed at this step using the TFN as follows: where ã ij = 1 , if i = j and ã ij =1,3,5,7,9 or ã ij =1 −1 ,3 −1 ,5 −1 ,7 −1 ,9 −1 where i ≠ j. After constructing the fuzzy comparison matrix, AHP method and a MATLAB program are used to calculate the weights of fuzzy AHP.
(1) www.nature.com/scientificreports/ Step 4: Get the judgments of the experts to evaluate the alternatives using Table 2, to obtain the group decision matrix X , where Ã (AI) and Ã (AAI) are the ideal and anti-ideal solutions, respectively.
Step 5: Normalize the X to obtain Ñ = ñ ij m×n as follows: Step 6: Obtain the weighted fuzzy matrix Ṽ where weight coefficients of the criterion ω j = ω l j , ω m j , ω u j are calculated using fuzzy-AHP method: Step 7: Calculate the utility degree K i : 77 Absolutely significant (AS) (6,7,8) 99 Absolutely more significant (AMS) (8,9,10) indicates the addition of elements of Ṽ : Step 8: Determine the utility functions for ideal f (K + i ) and anti-ideal f (K − i ) solutions as follows: Step 9: Calculate the utility functions f (K i ) to determine the rank of the alternatives:

Application of the proposed methodology
This section explains the HM power grid and its effect on the power system security. Following that, the conducted case study is illustrated.

Introduction of HM power grid.
In this section, the power system security is evaluated considering the actual specifications of HM power grid in China, which is a mainland city with a wealth of new energy resources. The HM power grid located in the hub of the "silk road" the ancient times. The unique natural environment makes the HM power grid extremely rich in wind and solar energy resources. In addition, it has a vast area and relatively flat terrain, where large scale wind farms and photovoltaic farms are distributed, and the distribution scale is gradually expanding. Moreover, HM is the first cross-regional UHV transmission channel to absorb wind power and other new energy resources in Northwest China. Also, it facilitates the first new energy and thermal power bundling through UHVDC power transmission project in China 49 .
According to the 13th five-year plan of HM Region, it was expected that the installed capacity of wind power would reach 12,100 MW and that of photovoltaic power would reach 9000 MW by 2020, of which the growth rate from 2012 to 2019 would increase year by year. Figure 3 shows the growth rate curve of wind and photovoltaic power installed capacity at HM power grid. The wind power scale and photovoltaic installed capacity of HM region continued to grow rapidly from 2012 to 2019, where the growth rate of wind power installed capacity was greater than that of the photovoltaic power. It can be seen that HM region, as the main gathering place of wind energy, is the key to new energy power generation in the whole China. As a hub connected with the mainland power grid, the energy security of HM region evidently affects the energy security of the whole China power system transmission.  Case study. After gathering the SWOT factors, organizations usually use the AHP method to quantify the priority order of strategies and calculate the weights of the factors. The SWOT matrix and its hierarchical structure constructed by 24 factors and 8 improvement strategies are shown in Fig. 4. A group of experts determine the priorities of SWOT dimensions and factors based on Table 1. The calculated weight values calculated and the results are given in Tables 3, 4 The ranked order of SWOT is obtained as S > O > T > W. Through the strengths of HM power grid, seizing more opportunities and daring to threats will effectively overcome the weaknesses and make the online education more successful. Here, the ranked order of the strength factors is obtained as S3 > S6 > S5 > S2 > S1 > S4. Firstly, vigorously develop the rich potential of new energy resources in HM power grid and develop the local new energy resources through advanced technology. Secondly, through the support of government policies and investment, reduce the cost of power production and benefit the public. Furthermore, the ranked order of the weakness factors is obtained as W3 > W1 > W6 > W2 > W4 > W5. Due to long service time of power grid equipment, coupled with the strong uncertainty of random fluctuation of new energy itself and the impact of quarterly changes on   www.nature.com/scientificreports/ new energy, the system is prone to collapse and various faults, thus affecting the normal operation and power generation of the power system, which corresponds to an inevitable weakness of the HM power grid. Progressively, the ranked order of the opportunity factors is obtained as O2 > O1 > O6 > O4 > O3 > O5. By expanding the government policies, financial support and bidding opportunities, we will enable economic and technical support for the development of new energy, vigorously develop the undeveloped new energy, reduce the power production cost of new energy, and bring the economic and social benefits to the society. Lastly, the ranked order of the threat factors is extracted as T1 > T2 > T5 > T3 > T6 > T4. For North China power grids, especially the HM power grid, large-scale long-distance transmission, "West to East power transmission", is not only a great project, but    Table 7. Evaluation criteria of the Threats. (C.R. = 0.077). T1  T2  T3  T4  T5  T6  T1  T2  T3  T4  T5  www.nature.com/scientificreports/ also a great technical challenge. The strong randomness of load and the lack of appropriate power transmission planning leads to power transmission security problems. At the same time, such power transmission requires strong support from economy, technology and government policies. The alternative strategies shown in Fig. 4 are evaluated using the MARCOS method over the SWOT factors by the experts using linguistic terms given in Table 2, to obtain a group decision matrix given in Table 8.

Local weights
The extended initial fuzzy matrix X of MARCOS method is first created, including fuzzy anti-ideal Ã (AAI) and ideal Ã (AI) solutions. Extended initial fuzzy matrix is then normalized based on the benefit criteria of the proposed SWOT model in step 7. Here, all SWOT factors are benefit criteria. The weighted fuzzy matrix Ṽ created using global weights of the SWOT factors is given in Fig. 6. The utility degree K j , Ã j values, utility functions for the ideal f (K + j ) and anti-ideal f (K − j ) solutions, and T j values of alternative strategies are calculated and provided in Table 9. In addition, the defuzzification of values and utility functions f (K j ) of alternative strategies are obtained and the results are given in Table 10. The ranked order of the strategies is obtained as The results of this study essentially demonstrated that the most important dimensions that the State Grid should focus on are the strengths and opportunities concerning the HM power grid, where the internal and  www.nature.com/scientificreports/ external factors have almost the same importance. Therefore, we strive to maximize our strengths, weaken our weaknesses, dare to threats and seize the opportunities. Moreover, the ranked order of the strategies reveals that the three most important digital transformation strategies are A 2 , A 6 and A 5 . These three strategies are defined as "improving the technical establishment to encourage efficient and cheap electricity production", "strive to build local permanent load and reduce the risk of long-distance and high-capacity transmission", and "taking advantage of government incentives and investment to modify the irrational energy policies and energy planning", respectively.
Comparative analysis. This section provides the comparative analysis that is conducted to validate the proposed methodology. The comparison is made against the VIKOR and TOPSIS methods. Computational steps of VIKOR 20 and TOPSIS 32 are performed, and the corresponding results of VIKOR and TOPSIS are given in Tables 11 and 12, respectively. Besides, the utility function distribution in a three-dimensional space is shown in Fig. 6. Furthermore, the ranked orders of the alternatives obtained from fuzzy VIKOR, TOPSIS, and MARCOS methods are compared in Fig. 7, which are found as VIKOR-- According to the results, the solutions from these three compared methods Table 9. Obtained Ã j , Kj ( K − j ,K + j ) and T j values.  Table 10. Results of fuzzy MARCOS method and ranked order of the strategies. Sensitivity analysis. The sensitivity analysis can confirm the final prioritization of changes in priority weights of criteria. Table 13 shows the SWOT dimensions have ± 10%, ± 20%, and ± 30% ranking of global weights change. Following that, through the fuzzy MARCOS method, update the utility function F(K) values based on these weights. Next, ranked orders of the strategies alternatives are obtained based on the updated utility function values as shown in Fig. 8, which demonstrates the robustness and credibility of the MARCOS method. Furthermore, "improving the technical establishment to encourage efficient and cheap electricity production" is the most appropriate strategy in most cases.

Conclusion and perspective
New energy offers enormous potential to generate electricity in Northwest China regions, which could potentially be enough to meet overall China's energy demands. The vigorous development and utilization of new energy at HM power grid can not only reduce the dependence on traditional energy such as coal, oil and natural gas, but also improve the problem of energy shortage, create new employment opportunities, protect the natural environment, and make the rural regions with significant new energy potential wealthier. However, with the integration of new energy and microclimate-sensitive loads, power systems are becoming increasingly complex  Figure 7. Compared ranked orders of the strategies. www.nature.com/scientificreports/ and vulnerable to faults. As the main power generation area of Northwest China power grid, the safe and economic operation of HM power grid is becoming a more important and complex problem in the field of power system security operation. The strategic evaluation of this paper shows that the proposed method can be effectively used to determine the best strategies with highest priority, and illustrates the importance of establishing the right strategy to exploit a significant developing opportunity and highlight the strength of rapidly growing new energy power grid. The major contributions of this paper can be summarized as follows: • This article is the first study focusing on SWOT-AHP-MARCOS method for new energy power system operation security. • This study contributes to the HM power grid security operation prospective strategy selection problem by developing a new evaluation model. The effectiveness of the presented approach is validated via comparative analysis and sensitivity analysis. The results as follow: It is concluded that the three most important strategies are A 2 , A 6 and A 5 . These are "improving the technical establishment to encourage efficient and cheap electricity production", "strive to build local permanent load and reduce the risk of long-distance and high-capacity transmission", and "taking advantage of government incentives and investment to modify the irrational energy policies and energy planning", respectively. Northwest region is a poor area in China with underdeveloped economy. Although it has a great potential for new energy, this energy cannot be consumed locally. Therefore, the government advocates the policy of "power transmission from the west to the East" to invest in the energy field in the northwest region. First, it aims to solve the problem of energy shortage in the eastern developed regions. Second, it aims to promote the economic development of the northwest region through the advantages of high new energy storage, so as to achieve the "Chinese dream" of energy coexistence and common prosperity. In this regard, the results of the presented SWOT analysis showed that despite various challenges, HM power grid could still provide numerous benefits to the country over conventional non-new energy resources in terms of production cost, environmental aspects with additional prospects of endless new energy potential, which will greatly promote the economic development of Northwest China.
In the future, it is worthwhile to further study the following aspects: • The MCDM methods such as HFL-AHP, ANP, CM, CRITIC, DEA, ELECTRE, MABAC, TOPSIS, and VIKOR can be applied to the similar-type of decision-problem. • Based on the construction of SWOT index system, the method in this paper can be used to evaluate the power system development prospect among different regions in the world.
However, one of the limitations of this study is the identification of the items within the SWOT factors. During the process, the researchers' subjectivity may have affected the results. We believe that if the items were derived directly through interviews with experts and the top four items among them were selected, we could secure more objective results.

Data availablity
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.